Method of plating chromium and the like to titanium, its alloys, and the like



3,065,154 Patented Nov. 20, 1962 s tl65,154

Mitrnon or rraruito erruoMiUM AND THE firm To TITANIUM, rrs ALaoYs, AND THE Harold J. Wiesner, South Bend, 1nd,, assignor to The Bendix Corporation, a corporation of Delaware No Drawing. Filed June 25), 1959, Ser. No. 823,359 7 Claims. ((11. 204-452) The present invention relates to a method of plating those metals which form alkali metal and/ or alkaline earth metal, fluorine complexes; and more particularly to a method of plating chromium on titanium.

An object of the present invention is the provision of a new and improved method of plating those metals which form alkali metal and/ or alkaline earth halogen complexes and which are particularly troublesome to plate because of their aflinity for oxygen.

A more particular object of the invention is the provision of a new and improved method of plating upon metals which form alkali metal fluorine complexes.

A still more particular object of the invention is the provision of a new and improved method of plating upon titanium and zirconium metals and their alloys.

A most detailed object of the invention is the provision of a new and improved method of chrome plating upon titanium and its alloys.

Still other objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates from a reading of the following description of applicants preferred methods of practicing his invention, and his explanation of his discoveries and the principles which are involved therein.

Applicant has discovered that the formation in situ of alkali metal halogen complexes upon metals which readily oxidize breaks loose any oxide film present and forms a coating which is a complex of .the metal, which coating when properly formed, excludes oxygen sufficiently well to permit the metal to be transferred through the air to a plating bath without the formation of further troublesome oxide. He has further discovered that the nature of the complex formed in such that it dissolves readily and completely in acid plating baths so that the underlying metal is then exposed to the plating solution and does not interfere with the metal being deposited upon the basic metal surface.

After discovering that coatings of alkali metal fluorine complexes upon titanium were helpful in obtaining a good bond for a layer of chromium when electroplated upon the titanium, experimentation with various procedures helped applicant to arrive at the following steps as a preferred embodiment of his method of plating.

The article to be plated is sequentially:

(1) Sand blasted to remove scale and foreign matter.

(2) Immersed in an alkali metal halogen etching bath.

(3) Rinsed in distilled water.

(4) Stripped in a nonoxidizing acidic solution (preferably 50% hydrochloric).

(5 Rinsed in distilled water.

(6) Reimmersed in alkali metal halogen etching bath.

(7) Rinsed in distilled water. i

(8)' Immersed in electro-plating bath with current turned In general it has been found that the step of reimmersion inthe alkali metal halogen etching bath while not essential, helps to more completely rid the surface of all oxides, and provide a more uniform layer of complex. The purpose of the various rinsing steps is to prevent undue contamination of the etching and plating baths.

Early experiments in the formulation of the alkali metal halogen etching bath for the preparation of titanium and its alloys for plating has led applicant to the following preferred bath formulation:

Nal-ISO Approx. 235 grams/liter. NH F.HF Approx. 15 grams/liter. KF Approx. 50 grams/liter. HF (48% solution) Approx. milliliter/liter.

The purpose of the NaHSO, appears to be primarily one of supplying sodium ions. Other soluble salts of sodium can be used, providing its anion does not produce an oxidizing effect upon the metal to be plated. Rochelle salts (sodium potassium tartrate) trisodium phosphate have been used and found effective. The NH F.HF is not required but is found in'one commercially available source of the NaHSO used. The function of the KF is primarily to supply potassium ions. It also serves as a source of fluorine ions. The HP serves to provide both, the fluoride ion concentration, and the hydrogen ion concentration required. Sulfuric acid has been used with other fluoride ion containing salts to supply the hydrogen and fluoride ion concentrations.

It has been found that the concentration of hydrogen ion affects the thickness and density of the layer of complex formed upon the metal. Experience shows that the rate of formation of the complex layer increases generally as the hydrogen ion concentration is increased, and that the maximum thickness of the layer decreases as the hydrogen ion concentration increases above an optimum concentration. It appears that after a few minutes in the etching bath, an equilibrium is reached wherein the rate of formation of the complex equals the rate of its solution in the acid bath. As the hydrogen ion concentration of the bath is increased above the optimum, the more rapid dissolving of the layer decreases its maximum thickness. High alkali metal ion concentrations tend to promote the formation of dense complex layers. Applicant has found that an optimum thick dense complex layer can be ob tained by the incorporation of both sodium and potassium ions in the etching bath. Adding potassium ions to a sodium ion etching bath increases adhesion up to a point and thereafter seems to decrease the adhesion.

The rate of growth of the film appears to be controlled by time, temperature, and concentration; and temperatures of the etching bath can range from room temperature to the boiling point of the bath. The growth appears most rapid at the higher temperatures so that a temperature range of to 215 F. is very effective, and a range from to F. is preferred.

Inasmuch as chromium plating produces a hard non galling surface and, therefore, has great commercial potential, many plating tests were made of chromium deposits on titanium. Experience shows that practically any hard chrome plating bath can be used for the plating process, and one which applicant has found quite effective is made by a bath containing approximately 33.0 oz./ gal. of chromium trioxide and 0.33 oz./ gal of sulfate 1011.

In order to establish that applicants invention had universal application for titanium and its alloys, as many of the commercially available titanium alloys as could be obtained were tested. r a

Example I A 2 /2" diameter titanium alloy tube containing 4% vanadium and 6% aluminum was treated by the above listed preferred procedure. The tube was immersed in the etching bath for twenty minutes at 175 F., rinsed, immersed in an HCl stripping bath for one minute, reimmersed in the etching bath for ten minutes, rinsed, and then immersed in a chrome plating bath of the above preferred composition with the current turned on. The plating bath'had a temperature of approximatelyl30 F.,

and the bar was plated for approximately four hours at a current density of 2 to 3 amperes/ square inch to produce a chrome deposit of approximately 0.0035 inch thickness. The effectiveness of the adhesion of the plated layer was then determined by subjecting it to a Brinell hardness test using an Ms ball and a thousand kilogram load, and no spalling or flaking occurred.

An example of the use of a slightly different etching bath composition is as follows:

Example II A 3 /2" diameter titanium alloy tube containing 4% vanadium and 6% aluminum was sand blasted and etched in a bath of the following composition at 180 F. for five minutes:

Na PO .12H O Approx. 37 grams/liter. KP Approx. 20 grams/liter. HF (48%) Approx. 50 milliliters/liter.

The tube was then rinsed in deionized water, immersed 111 an electrochrome plating bath with the current turned on for five hours, at 130 F., and at approximately 2 amperes/ square inch current density to produce a plating thickness of approximately 0.0055 inch. The Brinell test produced no spalling or flaking.

Example III A Mallory-Sharon A-110AT titanium alloy bar containing 5% aluminum and 2% tin was treated substantially in accordance with the procedure outlined in Example I, and the adhesion as determined by the Brinell hardness test produced no spalling or flaking.

Example IV A titanium alloy bar containing 4% aluminum and 4% manganese was treated substantially according to the [procedure outlined in Example I. A quite violent reaction was noted to occur in the etching bath, and the complex coating did not appear to be as good as in the preceding examples. The chrome plating flaked ofi during the Brinell test and it is concluded that the manganese constituent was responsible to a quite violent reaction which caused a soft layer of complex to be formed which did not totally exclude oxygen from the base metal. Experience indicates that a more mild etching bath produced by decreasing the hydrogen ion concentration and/ or the potassium ion concentration in the etching bath would give improved results.

Example V A titanium alloy C-130 AM piece containing 4% aluminum and 4% manganese was etched in a bath of the following composition:

NaHSO Approx. 225 grams/liter. NH F.-HF Approx. grams/liter. KF Approx. 50 grams/liter. HF (48%) Approx. milliliters/liter.

for approximately twenty minutes at room temperature. The piece was thereafter immersed in a 50% HCl stripped solution for one minute; and immediately while wet placed in an electroless nickel plating bath .of the following approximate composition:

Grams/liter Nickel chloride 30 Sodium hypophosphite 10 Sodium hydroxyacetate 50 and a pH of approximately 5.6

for approximately one hour. The Brinell ball adhesion test produced no spalling or flaking of the nickel plating.

4, Example VI Zirconium alloy bars (Ziroalloy 2) containing 98% zirconium, l /2% tin and /2% minor impurities were etched in a bath of the following composition:

NaHSO Approx. 240 grams/liter. NH RHF 5 to 15 grams/liter. KF Approx. 30 grams/liter.

for approximately ten minutes at temperatures ranging from to P. All gave a white salt formation which flaked oil and the Zirconium was heavily pitted.

Another zirconium alloy bar of the same composition was given idential treatment except that the temperature of the bath was dropped to approximately 100 F. lt gave a good tightly adhering and uniform film of the type produced on the titanium.

Zirconium bars etched in the above manner were chrome plated in a hard chrome plating bath containing approximately 33.0 oz./gal. of chromium trioxide and 0.33 oz./gal. of sulfate ion for two hours at F. and a current density of 2 to 3 amperes/square inch. The above treatment gave a bright and uniform chrome plated layer approximately 0.002 inch thick.

Experience indicates that the zirconium is more reaci tive than the titanium, and that in general lower hydrogen ion concentrations and lower temperatures must be used in its etching baths than is used in the etching baths for titanium. Experience indicates that when the etching action is slowed down by reducing the temperature below approximately 100 F. and by using substantially no free hydrofluoric acid in the bath good etch films are produced, which films permit the zirconium to be satisfactorily plated.

While the invention has been described in considerable detail, I do not wish to be limited to the specific embodiments described; and it is my intention to cover hereby all novel adaptations, modifications and arrangements thereof which come within the practice of those skilled in the art to which the invention relates.

I claim:

1. A process for plating a metal on titanium and its alloys consisting of: immersing an article made of said titanium and its alloys in an etching solution consisting of a fluoride ion concentration above approximately 45 grams/liter, an alkali metal ion concentration of from about 40 grams/liter to 90 grams/liter, and a hydrogen ion concentration below a pH of approximately one, to form a titanium fluoride complex coating over the article; and thereafter immersing the coated article in a plating bath whose hydrogen ion concentration is above approximately 2 normal, and whose complex forming ion concentrations are considerably below the above mentioned concentrations.

2. A process for plating a metal on titanium and its alloys consisting of: immersing an article made of said titanium and its alloys in an etching solution consisting of a fluoride ion concentration above approximately 45 grams/ liter, a potassium ion concentration of from about 10 grams/liter to 20 grams/liter, another alkali metal ion concentration of from about 15 grams/liter to 45 grams/liter, and a hydrogen ion concentration below a pH of approximately one, to form a titanium fluoride complex coating over the article; and thereafter immersing the coated article in a plating bath whose hydrogen ion concentration is above approximately 2 normal, and whose complex forming ion concentrations are considerably below the above mentioned concentrations.

3. A process for a plating metal on titanium and its alloys consisting of: immersing an article made of said titanium and its alloys in an etching solution consisting of a fluoride ion concentration above approximately 45 grams/liter. a potassium ion concentration of from about 10 grams/liter to 20 grams/liter, sodium ion concentration of from about 15 grams/liter to 45 grams/liter. and a hydrogen ion concentration abo e a pH of approximately one, to form a titanium fluoride complex coating over the article; and thereafter immersing the coated article in a plating bath and whose complex forming ion concentrations are considerably below the above mentioned concentrations.

4. A process for chrome plating titanium and its alloys consisting of immersing an article made of said titanium and its alloys in an etching solution consisting of a fluoride ion concentration above approximately 45 grams/ liter, a potassium ion concentration of from about grams/liter to 20 grams/liter, sodium ion concentration of from about grams/liter to 45 grams/liter, and a hydrogen ion concentration above a pH of approximately one, to form a titanium fluoride complex coating over the article; and thereafter immersing the coated article in a chrome plating bath, and whose complex forming ion concentrations are considerably below the above mentioned concentrations.

5. A process for chrome plating titanium and its alloys consisting of immersing an article made of said titanium and its alloys in an etching solution consisting of a fluoride ion concentration above approximately 45 grams/ liter, a potassium ion concentration of from about 10 grams/ liter to grams/liter, sodium ion concentration of from about 40 grams/liter, and a hydrogen ion concentration below a pH of approximately one, to form a titanium fluoride complex coating over the article; immersing the article in an acid stripping bath to remove the layer of complex; immersing the article in an acid etching bath of the above described type to again form a titanium fluoride complex coating; and thereafter transferring the coated article to a nonoxidizing chrome electroplating bath, said article being made the cathode and being immersed in the chrome plating bath with the current turned on.

6. A process for chrome plating titanium and its alloys consisting of immersing an article made of said titanium and its alloys in an etching solution consisting of approximately 245 grams/liter of Nal-ISO approximately grams/liter KP, and approximately grams/liter of HP, at a temperature of approximately 200 F. to form a titanium fluoride complex coating over the article; immersing the article in an approximately 50% hydrochloric acid stripping solution; immersing the article in an acid etching bath of approximately the above composition to again form a titanium complex coating; and thereafter transferring the coated article to a nonoxidizing chrome electro-plating bath.

7. A process for chrome plating titanium and its alloys consisting of immersing an article made of said titanium and its alloys in an etching solution consisting of approximately 245 grams/liter of NaHSO approximately 5 grams/liter of NH F.HF, approximately 50 grams/liter KF, and approximately 60 grams/liter of HF, at a temperature of approximately 200 F. to form a titanium fluoride complex coating over the article; immersing the article in an approximately 50% hydrochloric acid stripping solution; immersing the article in an acid etching bath of approximately the above composition to again form a titanium complex coating; and thereafter transferring the coated article to a chrome bath, said article being made the cathode and being immersed in the plating bath with the current turned on.

References Cited in the file of this patent UNITED STATES PATENTS 2,829,091 Missel Apr. 1, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 3 O65, 154 November :20 1962 Harold L Wiesner It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 43, for in read am is column 2 line 4, for "NH FQHF" read NH FOHF column 3 line 62. for "stripped" read stripping column 4 line 13 for "identlal" read identical line 68 for a plating read plating a column 5 lines I and 2O and column 6 11116? 2 and lo after consisting of each occum euce insert a co 0m Signed and sealed this 23rd day of July I963a (SEAL) Attest:

ERNEST w. SWIDER DAVID D Attesting Officer Commissioner of Patents 

1. A PROCESS FOR PLATING A METAL ON TITANIUM AND ITS ALLOYS CONSISTING OF: IMMERSING AN ARTICLE MADE OF SAID TITANIUM AND ITS ALLOYS IN AN ETCHING SOLUTION CONSISTING OF A FLOURIDE ION CONCENTRATION ABOVE APPROXIMATELY 45 GRAMS/LITER, AN ALKALI METAL ION CONCENTRATION OF FROM ABOUT 40 GRAMS/LITER TO 90 GRAMS/LITER, AND A HYDROGEN ION CONCENTRATION BELOW A PH OF APPROXIMATELY ONE, TO FORM A TITANIUM FLUORIDE COMPLEX COATING OVER THE ARTICLE; AND THEREAFTER IMMERSING THE COATED ARTICLE IN A PLATING BATH WHOSE HYDROGEN ION CONCENTRATION IS ABOVE APPROXIMATELY 2 NORMAL, AND WHOSE COMPLEX FORMING ION CONCENTRATIONS ARE CONSIDERABLY BELOW THE ABOVE MENTIONED CONCENTRATIONS. 